"We have so much rain water everywhere," said Ron Ventura, a Ventura County Environmental Health Division supervisor, referring to heavy rain earlier this year and noting that mosquito complaints are being received daily on a county hotline. "We've seen sites in Ventura County that haven't held or retained water for several years. These recent rains have filled these areas."

The stagnant water creates a breeding site for mosquitoes. Health officials say more mosquitoes doesn't automatically mean more West Nile but should raise awareness of steps needed to combat the illness and other mosquito-borne viruses.

No cases of West Nile in dead birds or people have been confirmed in Ventura County this year, although California has seen its first case, with a person diagnosed in Kings County last month.

A year ago, seven people contracted West Nile in Ventura County, with 442 cases across California, according to California Department of Public Health records. The virus brings symptoms including fever, headaches, nausea and vomiting. In rare cases, it can cause encephalitis and meningitis.

"As the rainy season comes to any end and temperatures rise, we will see increased mosquito activity," said California Department of Public Health Officer Dr. Karen Smith, emphasizing the need to dump out standing water. "Removing water will help reduce overall mosquito numbers and protect family members and neighbors from mosquito bites and mosquito-borne diseases."

Another concern is Zika, a virus that can cause miscarriage, stillbirth and severe birth defects. Officials said there are no cases of the disease being spread by mosquitoes in California. But there have been 541 Zika cases in the state since 2015, all somehow related to travel involving countries where the disease is transmitted.

In Ventura County, there have been nine cases of Zika since 2015, all linked to travel, according to state records.

Although there hasn't been insect transmission in California, some health officials say people should be aware of the virus because the Aedes aegypti and Aedes albopictus mosquitoes that can carry Zika, if infected by biting a person carrying the virus, have been found in some areas including Ventura County neighbors, Kern and Los Angeles counties.

The mosquitoes have not yet been found in Ventura County.

Heavy rain can bring a heavy mosquito season, but it also spawns moving water that can stymie mosquito populations in storm drains and other underground water systems.

"The disease transmission will depend on temperatures," said Middleton, noting that hotter climes will bring more mosquitoes. West Nile levels also hinge on the number of infected birds.

Officials say the way to fight mosquito populations is to check and clear any containers of standing water, from an old tire to a dish placed under a potted plant. Clean and scrub bird baths and pet water bowls. Understand that mosquitoes can breed almost anywhere.

"Anything as small as a 2-liter bottle cap would collect enough rainwater," Ventura said.

People should also use mosquito repellent outdoors, wear long sleeves and long pants and check window screens to make sure there are no holes.